As an apparatus for analyzing (counting and/or classifying) particles in a sample liquid, particle analyzing apparatuses constituted to measure and analyze particles based on an electric resistance method (also called impedance method) or flow cytometry are known (patent documents 1, 2 and the like). In these particle analyzing apparatuses, a sample liquid is flown through a measuring flow path with a small bore diameter allowing passage of particles one by one (aperture in electric resistance method and flow cell in flow cytometry), and each one of the passing particles is electrically or optically measured in the measuring flow path. In a more specific example, a measuring flow path and a subsequent connecting conduit line are provided on a container called a measuring chamber, and the sample liquid in the measuring chamber is sucked and passes through the measuring flow path by the action of a sucking pump connected to the distal end portion of the connecting conduit line, during which the particles in the sample liquid are electrically and/or optically measured.
In the aforementioned particle analyzing apparatus, as a preferable sucking pump to suck the sample liquid in the measuring chamber through the connecting conduit line from the outside, a syringe device in which a piston inserted in a cylinder is driven by an actuator can be mentioned. FIG. 3 is a block diagram showing one embodiment of the constitution of the main part of a particle analyzing apparatus using the syringe device as the sucking pump. The particle analyzing apparatus shown in this Figure is an apparatus for particle analysis based on the electric resistance method, and the particle X10 to be analyzed is a blood cell and a sample liquid Y10 is a diluted specimen liquid (blood). As shown in this Figure, a measuring chamber 100 houses a sample liquid Y10 containing particle X10. A dispensing mechanism to supply a specimen liquid to the measuring chamber 100, a mechanism to supply a dilution liquid and a control device for controlling each part of the whole apparatus are not shown. An aperture 110 is provided as a measuring flow path on the wall of a lower part of the measuring chamber 100, and the measuring chamber communicates with a small chamber 120 adjacent to the outside through the aperture. Electrodes for the electric resistance method are provided in each of the measuring chamber and the small chamber to form an electrode pair (the electrodes are not shown). The small chamber 120 is connected to the syringe device 200 via a connecting conduit line C10. The conduit lines C30, C40 are pipes used for discharge and the like and normally closed. The syringe device 200 is constituted including a cylinder 210, a piston 220, and a reciprocating type actuator 230. The piston 220 reciprocates in the direction of the double-headed arrow in the drawing by the actuator 230, and sucking is performed when the piston is pulled (when moving upward in the Figure). When the syringe device 200 begins sucking, the blood cells X10 in the sample liquid Y10 in the measuring chamber 100 pass through the aperture 110 one by one as indicated by arrow, the measurement signal obtained by the electrode pair is sent to the control device, and various calculations for analysis of the blood cells are performed.
Patent Document 1: JP-A-2005-091098
Patent Document 2: JP-A-2016-024024
In the particle analyzing apparatus exemplified in FIG. 3, a method for sucking the sample liquid in the measuring chamber more preferably by a syringe device, the present inventors took note of and studied a method of sucking the sample liquid by the following procedures (i) to (iii) instead of a method of simultaneously sucking only a travel amount of the sample liquid Y10 while pulling the piston of the syringe device.
(i) First, the first valve 310 provided in the middle of the connecting conduit line C10 is closed, the second valve 320 provided in the middle of the conduit line C20 for opening the atmospheric pressure connected to the tip (lower part in the Figure) of the cylinder 210 of the syringe device 200 is opened, and the piston 220 is moved to the forward position (position L10 indicated by short dash line in FIG. 3) by pushing the piston 220. Here, the first and the second valves are, for example, electromagnetic valves that can be opened and closed by a command signal.
(ii) Then, the first valve 310 is closed and the second valve 320 is also closed, piston 220 is pulled to move the piston 220 to a predetermined backward position (position L20 shown with short dash line in FIG. 3) to create a predetermined volume of a space in the cylinder 210. The pressure in the predetermined volume of the space is, for example, a pressure about 20 kPa lower than the atmospheric pressure at that time (negative pressure).
(iii) Next, the first valve 310 is opened, the negative pressure in the cylinder is applied to the measuring flow path and the measuring chamber, and suction of the sample liquid is started.
The operation of the above steps (i)-(iii) is an operation in which the space of negative pressure having a particular volume for suction is created prior to suction, and the sample liquid in the measuring chamber is drawn into the space utilizing the negative pressure. Therefore, minute adjustment of the retraction amount (travel distance) of the piston is not necessary. As a result, while it is easy to control the piston movement, relatively stable suction force can be obtained by this operation.
However, when the present inventors studied the particle analyzing apparatus applying the operation of the above-mentioned steps (i)-(iii) in more detail, it was found that even when a space with a certain volume is created in a cylinder in the above-mentioned step (ii), the pressure in the space is not always the same, as a result of which the results of particle analysis also vary. Such a phenomenon may be caused by, among others, the following reason. That is, in a general syringe device, even if the piston is forwarded to the most distal position (the lowest point in FIG. 3) of the cylinder, a small space remains between the tip end surface of the piston and the inner wall surface of the cylinder, and a gas (air) at atmospheric pressure at that time remains. As a result, the pressure (negative pressure) in the space with a certain volume created in the cylinder by moving the piston backward varies mainly according to the atmospheric pressure at that time. Therefore, the pressure in the space in the cylinder produced when the user uses same differs by a trace amount from that in the space in the cylinder produced by the adjustment during the production of the particle analyzing apparatus. When sucking with an action of such different negative pressure is performed during use the user, the flow velocity of the sample liquid also varies. As a result, the measurement signals obtained for the same standard sample liquid vary between adjustment in a factory and use by the user. Accordingly, the particle analysis results obtained by calculating and processing such measurement signals also vary.
An object of the present invention is to solve the above-mentioned problem and provide a particle analyzing apparatus capable of particle analysis with less error by simple control while using a syringe device as a suction pump.